1. Field of the Invention
The present invention relates to a contents distribution system, a contents distribution method, and a terminal apparatus used therein. In particular, it relates to a contents distribution system, a contents distribution method, and a terminal apparatus used therein, which carry out a transmission and reception of a decoding key for decoding encoded contents data.
2. Description of the Related Art
In recent years, a contents distribution service which carries out a streaming distribution of contents data such as music, a movie, or a talk program, via a network such as an internet, has begun to be launched. As this kind of contents distribution system, a system called P2P (Peer to Peer) communication has been devised in which a terminal apparatus which receives contents data from a distribution source, as well as reproducing the contents data, sequentially relays the contents data to another terminal apparatus.
A format of a contents data distribution system according to this P2P communication is such that, providing a broadcasting station which distributes contents data, and a connection management apparatus (hereafter called a management server) which manages a connection condition of a network in which a plurality of terminal apparatus are logically connected, multi-layered in a hierarchical structure, with the broadcasting station as an apex, contents data distributed from the distribution system are sequentially relayed to a downstream terminal apparatus by means of a relaying function of the terminal apparatus, distributed to all of the plurality of terminal apparatus, and each terminal apparatus can reproduce the contents data received.
A plurality of broadcasting stations distributing contents data exist, one for each viewing or listening channel provided. A user, in a case of wishing to view or listen to a specified channel, can change a viewing or listening channel by switching to a broadcasting station which is carrying out a distribution of specified contents data according with the request.
In the event that contents to be previewed are charged, or in the event that a restriction is applied to a duplication or a transferal of a copyrighted work to be distributed, a method encoding contents to be distributed is used as a technology protection measure. With regard to a decoding key for decoding encoded contents, a method acquiring a decoding key from a key server which stores decoding keys when a terminal apparatus participates in a specified contents distribution system (refer to FIG. 18), or a method regularly inserting a decoding key between items of contents data, and distributing it along with the contents data (refer to FIG. 19), can be considered. For example, in Japanese Unexamined Patent Publication No. 2003-229843, a streaming system is disclosed wherein encoded contents key data for decoding encoded contents data are distributed to a client terminal along with the encoded contents data.